<div class="refentry" lang="en" xml:lang="en"><a id="glEvalPoint"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glEvalPoint — generate and evaluate a single point in a mesh</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glEvalPoint1</b>(</code></td><td>GLint  </td><td><var class="pdparam">i</var><code>)</code>;</td></tr></table></div><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glEvalPoint2</b>(</code></td><td>GLint  </td><td><var class="pdparam">i</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">j</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>i</code></em></span></dt><dd><p>
                    Specifies the integer value for grid domain variable
                    <math overflow="scroll"><mi mathvariant="italic">i</mi></math>.
                </p></dd><dt><span class="term"><em class="parameter"><code>j</code></em></span></dt><dd><p>
                    Specifies the integer value for grid domain variable
                    <math overflow="scroll"><mi mathvariant="italic">j</mi></math>
                    (<code class="function">glEvalPoint2</code> only).
                </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <a class="citerefentry" href="glMapGrid"><span class="citerefentry"><span class="refentrytitle">glMapGrid</span></span></a> and <a class="citerefentry" href="glEvalMesh"><span class="citerefentry"><span class="refentrytitle">glEvalMesh</span></span></a> are used in tandem to efficiently
            generate and evaluate a series of evenly spaced map domain values.
            <code class="function">glEvalPoint</code> can be used to evaluate a single grid point in the same gridspace
            that is traversed by <a class="citerefentry" href="glEvalMesh"><span class="citerefentry"><span class="refentrytitle">glEvalMesh</span></span></a>.
            Calling <code class="function">glEvalPoint1</code> is equivalent to calling
            </p><pre class="programlisting">
glEvalCoord1( <math overflow="scroll">

     	          <mrow>
     	              <mrow>
     	                  <mn>i</mn>
     	                  <mo>·</mo>
     	                  <mo>Δ</mo>
     	                  <mi mathvariant="italic">u</mi>
     	              </mrow>
     	              <mo>+</mo>
     	              <msub>
     	                  <mi mathvariant="italic">u</mi>
     	                  <mn>1</mn>
     	              </msub>
     	          </mrow>
              </math> );
         </pre><p>
            where
            </p><div class="informalequation"><math overflow="scroll">

                <mrow>
                    <mrow>
                        <mo>Δ</mo>
                        <mi mathvariant="italic">u</mi>
                    </mrow>
                    <mo>=</mo>
                    <mfrac>
                        <mfenced open="(" close=")">
                            <mrow>
                                <msub><mi mathvariant="italic">u</mi>
                                <mn>2</mn>
                                </msub>
                                <mo>-</mo>
                                <msub><mi mathvariant="italic">u</mi>
                                <mn>1</mn>
                                </msub>
                            </mrow>
                        </mfenced>
                        <mi mathvariant="italic">n</mi>
                    </mfrac>
                </mrow>
            </math></div><p>
        </p><p>
            and
            <math overflow="scroll"><mi mathvariant="italic">n</mi></math>,
            <math overflow="scroll">

                <msub><mi mathvariant="italic">u</mi>
                <mn>1</mn>
                </msub>
            </math>,
            and
            <math overflow="scroll">

                <msub><mi mathvariant="italic">u</mi>
                <mn>2</mn>
                </msub>
            </math>
            are the arguments to the most recent <a class="citerefentry" href="glMapGrid1"><span class="citerefentry"><span class="refentrytitle">glMapGrid1</span></span></a> command.
            The one absolute numeric requirement is that if
            <math overflow="scroll">

                <mrow>
                    <mi mathvariant="italic">i</mi>
                    <mo>=</mo>
                    <mi mathvariant="italic">n</mi>
                </mrow>
            </math>,
            then the value computed from
            <math overflow="scroll">

                <mrow>
                    <mrow>
                        <mi mathvariant="italic">i</mi>
                        <mo>·</mo>
                        <mrow>
                            <mo>Δ</mo>
                            <mi mathvariant="italic">u</mi>
                        </mrow>
                    </mrow>
                    <mo>+</mo>
                    <msub><mi mathvariant="italic">u</mi>
                    <mn>1</mn>
                    </msub>
                </mrow>
            </math>
            is exactly
            <math overflow="scroll">

                <msub><mi mathvariant="italic">u</mi>
                <mn>2</mn>
                </msub>
            </math>.
        </p><p>
            In the two-dimensional case, <code class="function">glEvalPoint2</code>, let
        </p><p>
            </p><div class="informalequation"><math overflow="scroll">

                <mrow>
                    <mrow>
                        <mo>Δ</mo>
                        <mi mathvariant="italic">u</mi>
                    </mrow>
                    <mo>=</mo>
                    <mfrac>
                        <mfenced open="(" close=")">
                            <mrow>
                                <msub><mi mathvariant="italic">u</mi>
                                <mn>2</mn>
                                </msub>
                                <mo>-</mo>
                                <msub><mi mathvariant="italic">u</mi>
                                <mn>1</mn>
                                </msub>
                            </mrow>
                        </mfenced>
                        <mi mathvariant="italic">n</mi>
                    </mfrac>
                </mrow>
            </math></div><p>
            </p><p>
                </p><div class="informalequation"><math overflow="scroll">

                    <mrow>
                        <mrow>
                            <mo>Δ</mo>
                            <mi mathvariant="italic">v</mi>
                        </mrow>
                        <mo>=</mo>
                        <mfrac>
                            <mfenced open="(" close=")">
                                <mrow>
                                    <msub><mi mathvariant="italic">v</mi>
                                    <mn>2</mn>
                                    </msub>
                                    <mo>-</mo>
                                    <msub><mi mathvariant="italic">v</mi>
                                    <mn>1</mn>
                                    </msub>
                                </mrow>
                            </mfenced>
                            <mi mathvariant="italic">m</mi>
                        </mfrac>
                    </mrow>
                </math></div><p>
            </p><p>
        </p><p>
            where
            <math overflow="scroll"><mi mathvariant="italic">n</mi></math>,
            <math overflow="scroll">

                <msub><mi mathvariant="italic">u</mi>
                <mn>1</mn>
                </msub>
            </math>,
            <math overflow="scroll">

                <msub><mi mathvariant="italic">u</mi>
                <mn>2</mn>
                </msub>
            </math>,
            <math overflow="scroll"><mi mathvariant="italic">m</mi></math>,
            <math overflow="scroll">

                <msub><mi mathvariant="italic">v</mi>
                <mn>1</mn>
                </msub>
            </math>,
            and
            <math overflow="scroll">

                <msub><mi mathvariant="italic">v</mi>
                <mn>2</mn>
                </msub>
            </math>
            are the arguments to the most recent <a class="citerefentry" href="glMapGrid2"><span class="citerefentry"><span class="refentrytitle">glMapGrid2</span></span></a> command.
            Then the <code class="function">glEvalPoint2</code> command is equivalent to calling
            </p><pre class="programlisting">
glEvalCoord2( <math overflow="scroll">

		        <mrow>
			    <mrow>
			        <mn>i</mn>
				<mo>·</mo>
			        <mo>Δ</mo>
		                <mi mathvariant="italic">u</mi>
			    </mrow>
		            <mo>+</mo>
		            <msub>
		                <mi mathvariant="italic">u</mi>
		                <mn>1</mn>
		            </msub>
			    <mo>,</mo>

			    <mrow>
			        <mn>j</mn>
				<mo>·</mo>
			        <mo>Δ</mo>
		                <mi mathvariant="italic">v</mi>

			    </mrow>
		            <mo>+</mo>
		            <msub>
		                <mi mathvariant="italic">v</mi>
		                <mn>1</mn>
		            </msub>
			</mrow>
		    </math> );
            </pre><p>
            The only absolute numeric requirements are that if
            <math overflow="scroll">

                <mrow>
                    <mi mathvariant="italic">i</mi>
                    <mo>=</mo>
                    <mi mathvariant="italic">n</mi>
                </mrow>
            </math>,
            then the value computed from
            <math overflow="scroll">

                <mrow>
                    <mrow>
                        <mi mathvariant="italic">i</mi>
                        <mo>·</mo>
                        <mrow>
                            <mo>Δ</mo>
                            <mi mathvariant="italic">u</mi>
                        </mrow>
                    </mrow>
                    <mo>+</mo>
                    <msub><mi mathvariant="italic">u</mi>
                    <mn>1</mn>
                    </msub>
                </mrow>
            </math>
            is exactly
            <math overflow="scroll">

                <msub><mi mathvariant="italic">u</mi>
                <mn>2</mn>
                </msub>
            </math>,
            and if
            <math overflow="scroll">

                <mrow>
                    <mi mathvariant="italic">j</mi>
                    <mo>=</mo>
                    <mi mathvariant="italic">m</mi>
                </mrow>
            </math>,
            then the value computed from
            <math overflow="scroll">

                <mrow>
                    <mrow>
                        <mi mathvariant="italic">j</mi>
                        <mo>·</mo>
                        <mrow>
                            <mo>Δ</mo>
                            <mi mathvariant="italic">v</mi>
                        </mrow>
                    </mrow>
                    <mo>+</mo>
                    <msub><mi mathvariant="italic">v</mi>
                    <mn>1</mn>
                    </msub>
                </mrow>
            </math>
            is exactly
            <math overflow="scroll">

                <msub><mi mathvariant="italic">v</mi>
                <mn>2</mn>
                </msub>
            </math>.
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>
            <a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP1_GRID_DOMAIN</code>
        </p><p>
            <a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP2_GRID_DOMAIN</code>
        </p><p>
            <a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP1_GRID_SEGMENTS</code>
        </p><p>
            <a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_MAP2_GRID_SEGMENTS</code>
        </p></div>
        {$pipelinestall}{$examples}
        <div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a class="citerefentry" href="glEvalCoord"><span class="citerefentry"><span class="refentrytitle">glEvalCoord</span></span></a>,
            <a class="citerefentry" href="glEvalMesh"><span class="citerefentry"><span class="refentrytitle">glEvalMesh</span></span></a>,
            <a class="citerefentry" href="glMap1"><span class="citerefentry"><span class="refentrytitle">glMap1</span></span></a>,
            <a class="citerefentry" href="glMap2"><span class="citerefentry"><span class="refentrytitle">glMap2</span></span></a>,
            <a class="citerefentry" href="glMapGrid"><span class="citerefentry"><span class="refentrytitle">glMapGrid</span></span></a>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>
            Copyright © 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.
        </p></div></div></div>
